Hello. Hello. Anyone There?

Q. Why does my phone sometimes ring and when I pick up, no one is there? There’s no hang-up click, and the phone company says my line works fine.

A. If dead silence follows your “hello,” it’s likely the call is from a telemarketing center using “predictive dialing” technology, in which a computer dials multiple phone numbers over a short period.

When you answer, the computer is meant to quickly transfer you to an available telemarketer, and the usual sales pitch follows. But if all sales reps are occupied with other calls, you hear nothing.

Other times, these “abandoned” calls are prerecorded pitches that will not begin unless you speak loudly enough or in some cases say “hello” twice.

Although they continue, most sales-related robocalls have been illegal since September 2009 unless the caller gets previous written permission from the recipient. However, exemptions include robocalls from charities, politicians, banks and telephone carriers, along with “informational” messages about school and road closings, flight delays and service appointments.

If you’re bothered by these calls, the Privacy Rights Clearinghouse recommends that you contact the so-called annoyance office of your phone company and request that a “trap” be placed on your line, which will allow calls to be traced. You’ll have to note the time and date of abandoned or other bothersome calls, but traps are usually free, and in some cases the phone company will contact offenders on your behalf.

There are also gizmos, costing about $40 and available online and at electronics stores, that are designed to cut off computerized telemarketing calls, but the devices get mixed reviews.

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Sid Kirchheimer writes about consumer and health issues.